Machines, such as, for example, track-type tractors and other construction, agriculture, and mining machines, are used to perform many tasks. To effectively perform these tasks, such machines require a power source that provides significant power to a drive system. The power source may be an engine such as, for example, a turbine engine, diesel engine, gasoline engine, or natural gas engine operated to generate a torque output at a range of speeds. This torque is typically provided to one or more traction devices via a transmission operably connected to the engine via the drive system.
To assist the transmission and the engine in satisfying the varying requests of the traction devices during use, the drive systems of such machines typically include one or more motors, torque converters, or other like devices configured to supply supplemental torque to the transmission in certain situations. For example, such drive system components may be configured to supplement the torque provided by the engine during machine operations in which wide, relatively rapid variations in the transmission output speed are required.
An exemplary drive system is described in U.S. Pat. No. 5,168,946 (the '946 patent) issued to Dorgan on Dec. 8, 1992. The '946 patent describes an electric drive system having first, second, and third electric motors connected via left and right combining gear sets to respective left and right vehicle tracks. To propel the vehicle in low range operations (e.g., low speed, high torque), the first and second motors are energized, while the a brake is applied to the third motor. To propel the vehicle in high range operations (e.g., high speed, low torque), all three motors are energized. As explained in the '946 patent, the use of three motors, rather than two, in high range operations results in a reduction of motor sizes.
Although the drive system disclosed in the '946 patent may be used to propel the vehicle in a number of operating ranges, drive systems of the type disclosed in the '946 patent have a variety of drawbacks. For example, in order to account for occasional high-torque and/or high power loading situations, the motors and/or other components of such drive systems are typically oversized for a majority of the machine operation. In addition to the high cost of such components, and the related packaging issues, operation of these oversized drive system components during low-torque loading conditions is inefficient. Moreover, such components are known to be inefficient due to the torque losses associated with their operation. Additionally, such components are not configured to facilitate the storage of energy received from the transmission and/or the engine during operations in which, for example, excess torque has been generated by the engine. Instead, such known drive system components typically transform such excess energy to heat. Over time, such heat generation can cause damage to these drive system components, and may result in their premature failure.
The disclosed systems and methods are directed to overcoming one or more of the problems set forth above.